1. Field of the Invention
The present invention relates to a thermoplastic and injectable endodontic filling composition which shows an excellent resilience and does not shrink after insertion into a dental root canal.
2. Description of the Related Art
The standard technique in obturating a dental root canal involves the insertion of filling composition into a prepared root canal. Commercially known endodontic filling compositions usually comprise a mixture of balata, zinc oxide, heavy metal sulfates and wax. These balata-based cones have been in common usage for many years. However, it is not always introduced easily into a root canal. Following introduction of the filling composition into the canal, a spreader is used to condense the composition both laterally and vertically to produce a close arrangement of the filling material to the root canal. The spreader may be heated in order to assist in this operation.
Accordingly, a need exists for an endodontic filling composition which does not shrink after insertion into a root canal. Additionally, in order to be feasible, the endodontic filling composition must possess physical properties which facilitate its introduction into the prepared root canal. Specifically, the composition must be extrudable so as to be injectable into the root canal at an elevated, but clinically acceptable, temperature. However, the composition must solidify at body temperature after placement in the root canal.
The prior art has attempted to formulate a thermoplastic endodontic filling composition. For example, U.S. Pat. No. 4,483,679 to Fujisawa et al. discloses thermoplasticized endodontic filling materials which are injectable at clinically acceptable conditions. The compositions of this patent comprise mixtures of balata or isoprene polymer and paraffin wax to provide filling compositions with relatively low softening temperatures.
U.S. Pat. No. 4,632,977 to Riazi discloses a process for altering the thermoplasticity of balata or isoprene polymer to produce a dental filling composition which is injectable by a manual syringe at clinically acceptable temperatures. The process involves a heat treatment during which a high shear force is applied to molten polymer to masticate and clip the chain length of the polymer until the melt index of the polymer reaches 50.0 gm/min.
The endodontic filling compositions produced according to these patents, however, is costly to manufacture and lack the resilience of the conventional gutta percha cone. Thus it is desirable to produce an endodontic filling material that is easily introduced into a prepared root canal and which seals the canal laterally and vertically without shrinkage.